1. Field of the Invention
This invention relates to the conversion of non-ferrous metal mattes to the metal or metal sulphide.
2. Description of the Prior Art
The Pierce-Smith converter has been used widely for this purpose, since the turn of the twentieth century, and so converting in this vessel will be used to exemplify the present invention. The operation of this apparatus is described in some detail in Extractive Metallurgy of Copper by Newton, Chapter V, Converting; in Extractive Metallurgy of Sulfide Ores by J. Boldt and P. Queneau, pages 249-252 (1967) and more of the complexities of the converting operation may be found in papers such as "Metallurgy of the Converting Process in the Thompson Smelter," a paper prepared for presentation at the 14th Annual Conference of Metallurgists, Edmonton, Alberta in August 1975, the contents of these publications being hereby incorporated by reference.
Fundamentally, the Pierce-Smith converter is made up of a horizontal cylinder providing within it an elongated sealed refractory lined chamber having a cylindrical sidewall and circular endwalls. The sidewall is provided with a hooded opening for charging and discharging located between the endwalls and a row of injection pipes, or tuyeres, entering the chamber through the refractory lining at one side. The vessel is rotated between a charging position in which the opening is accessible from the side that it can be charged and a blowing position in which the charging opening faces upward and is hooded and forms an off-gas outlet. With the vessel in blowing position air or air slightly enriched with oxygen is blown in through the tuyeres at low pressure, typically 15 psig to oxidize iron and sulfur in the matte and, thus, effect separation from the matte to form slag and release off-gases, namely, sulfur dioxide. The iron is converted to iron oxide, fluxed with silica and removed as a slag while the sulfur is oxidized to sulfur dioxide which leaves the converter in the off-gas. Further details of the converting operation in the Pierce-Smith converter are contained in the publications referred to and some of the complexities of chemical reactions, heat transfer and other relatively complex changes in conditions are described. Through the many years of operation of this type of converter, a manner of operation has developed which has undergone little change in the past few years.
There are certain disadvantages that have always plagued the use of this converter. For example, the tuyeres become plugged quickly and thus require clearing on a regular basis by punching with a metal rod which is forced through the tuyere. Another problem is that severe refractory wear occurs along the tuyere line, above the tuyeres in the backwall and the endwalls. This refractory wear is sufficiently excessive that a converter typically operates for only three months out of four, the other month being required for refractory repair. This results in high maintenance costs and necessitates excess converter capacity in a smelter operation. A further problem is accretion build-up in the converter mouth, resulting from the accumulation of particles entrained in the off-gases and which is a function of the airflow. This build-up requires frequent cleaning. These problems seem to have been accepted as a fact of life in non-ferrous metal converting using the Pierce-Smith converter.
Attempts to improve refractory life have been in the area of using better, more wear-resistant refractories as for instance discussed in "The Copper Refractory Symposium" held in New York in 1968. At that Symposium various factors were described which adversely affect refractory life and which must be controlled, for example, wide rapid temperature variations, low-grade matte with resultant large slag volumes, fine or extremely coarse flux, punching and fluxing practice, low blowing rates, methods of cleaning the converter mouth, and modifying the normal converter heating periods.